The field of the invention is filtration systems.
Filtration systems often require substantial pressure to drive a fluid through a membrane or other filter. In the case of reverse osmosis systems, this pressure requirement can translate into a substantial energy cost or xe2x80x9cpenalty.xe2x80x9d
It is known to mitigate the energy cost of filtration pumping by employing a work exchange pump such as that described in U.S. Pat. No. 3,489,159 to Cheng et al. (January 1970) which is incorporated herein by reference. In such systems, pressure in the xe2x80x9cwastexe2x80x9d fluid that flows past the filter elements is used to pressurize the feed fluid. Unfortunately, known work exchange pumps employ relatively complicated piping, and in any event are discontinuous in their operation. These factors add greatly to the overall cost of installation and operation.
It is also known to mitigate the energy cost of filtration pumping on a continuous basis by employing one or more turbines to recover energy contained in the xe2x80x9cwastexe2x80x9d fluid. A typical example is included as FIG. 3 in PCT/ES96/00078 to Vanquez-Figueroa (publ. October 1996), which is also incorporated herein by reference. In that example, a feed fluid is pumped up a mountainside, allowed to flow into a filtration unit partway down the mountain, and the waste fluid is run through a turbine to recover some of the pumping energy.
A more generalized schematic of a prior art filtration system employing an energy recovery turbine is shown in FIG. 1. There a filtration system 10 generally comprises a pump 20, a plurality of parallel permeators 30, an energy recovery turbine 40, and a permeate or filtered fluid holding tank 50. The fluid feed lines are straightforward, with an intake line (not shown) carrying a feed fluid from a pretreatment subsystem (not shown) to the pump 20; a feed fluid line 22 conveying pressurized feed fluid from the pump 20 to the permeators 30; a permeate collection line 32 conveying depressurized permeate from the permeators 30 to the holding tank 50; a waste fluid collection line 34 conveying pressurized waste fluid from the permeators 30 to the energy recovery turbine 40; and a waste fluid discharge line 42 conveying depressurized waste fluid from the energy recovery turbine 40 away from the system 10.
A system according to FIG. 1 may be relatively energy efficient, but is still somewhat complicated from a piping standpoint. Among other things, each permeator 30 has at least three high pressure fluid connectionsxe2x80x94one for the feed fluid, one for the waste fluid, and one for the permeate. In a large system such fluid connections may be expensive to maintain, especially where filtration elements in the permeators need to be replaced every few years.
Thus, there is a continuing need for a simplified approach to recovering energy costs employed in pressurizing a filtration system.
The present invention is directed to filtration systems in which a plurality of filtration modules disposed within an outer casing produce both a low pressure filtrate and a high pressure waste fluid from a feed fluid, and energy in the high pressure waste fluid is used to pressurize the feed fluid.
In preferred embodiments the feed fluid is pressurized using a pressurization subsystem, the energy in the waste fluid is recovered using an energy recovery subsystem, and the pressurization and energy recover subsystems are mechanically coupled such that energy derived from the energy recovery subsystem is used to drive the pressurization subsystem. In more preferred embodiments at least one of the pressurization and energy recovery subsystems utilize a turbine. In still more preferred embodiments the pressurization and energy recovery subsystems are coupled using a common drive shaft.
Various objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the invention, along with the accompanying drawings in which like numerals represent like components.